1. Field of the Invention
This invention relates to a process for making manganese, electrolytic manganese dioxide, and specifically, the electrolytic process for making manganese, electrolytic manganese dioxide and MnO.sub.2 wherein a source of manganomanganic oxide (Mn.sub.3 O.sub.4) is treated in a leach solution in the presence of a reducing agent to convert the manganomanganic oxide to manganese sulfate. The leach solution is then treated to conventional purification and electrowinning steps to recover the manganese.
2. Prior Art
The electrolytic process is used to make a high purity (99.5%) manganese metal. Conventionally, a source of manganese oxide (MnO) is leached with sulfuric acid at a pH of 3 to convert the manganese oxide to manganese sulfate (MnSO.sub.4). The leach solution is water based and manganese sulfate is soluble in the leach solution.
Conventionally, the source of manganese oxide is either a manganese ore which has been roasted to reduce the higher oxides of manganese (e.g. MnO.sub.2, Mn.sub.2 O.sub.3 and Mn.sub.3 O.sub.4) to manganese oxide (MnO); or a slag obtained from a high carbon ferromanganese smelting operation. The slag contains manganese oxide. In either case, the conventional starting material for the electrolytic process is manganese oxide (MnO).
The purification of the leach solution is conducted to remove the other metals as precipitates. The aqueous leach solution is then neutralized with ammonia to a pH of 6-7 to precipitate the iron and aluminum which are later removed by filtration. A sulfide, usually hydrogen sulfide gas, is also added to the leach solution to precipitate the heavy metals such as arsenic, copper, zinc, lead, cobalt and molybdenum as sulfides which are also conventionally removed by filtration. Ferrous sulfide or ammonium sulfide plus air is added to the leach to remove colloidal sulfur, colloidal metallic sulfides and organic matter. Again, it is conventional to use filtration to remove these colloidal and organic materials.
Finally, the leach solution is added to an electrolytic cell and manganese metal from the leach solution deposits on the cathode. A high purity (99.5%) manganese is recovered from the cathode in a conventional manner.